1. Field of the Invention
The present invention relates to filters, and more particularly, to a filter for a fluid actuating device in an automatic transmission primarily intended for motor vehicle use.
2. Description of Related Art
A conventional transmission includes a hydrodynamic torque convertor to transfer engine torque from an engine crankshaft to a rotatable input member of the transmission through fluid-flow forces. The transmission includes frictional units which couple the rotatable input member to one or more members of a planetary gear set. Other frictional units, typically referred to as brakes, hold members of the planetary gear set stationary during flow of power. These frictional units are usually brake clutch assemblies or band brakes. The drive clutch assemblies can couple the rotating input member of the transmission to the desired elements of the planetary gear set, while the brakes hold elements of these gear sets stationary. Such transmission systems also typically provide for one or more fluid actuating devices such as a piston in order to engage and disengage the frictional units.
Automatic transmissions are designed to take automatic control of the frictional units, gear ratio selection and gear shifting. An example of such an automatic transmission is disclosed in copending patent application, Ser. No. 188,610, filed Apr. 29, 1988 now U.S. Pat. No. 4,964,506 and assigned to the assignee of the present application. In this automatic transmission, fluid actuating devices such as pressure balanced pistons are provided to prevent the centrifugal force acting on the rotating fluid in the clutch cavity from causing the piston to remain in a clutch apply position even though fluid apply line is vented. More specifically, the pressure balance pistons have an orifice to allow fluid to pass therethrough due to differential pressure.
One disadvantage with the above pressure balanced pistons is that if a filter is not provided in the orifice, the orifice may be plugged by contaminants in the transmission fluid. As a result, a need exists for providing a filter that is bidirectional for allowing fluid to pass therethrough.
It is, therefore, one object of the present invention to provide a bidirectional filter assembly for a pressure balanced piston.
It is another object of the present invention to provide a bidirectional filter assembly which can be used in various applications.
It is yet another object of the present invention to provide a bidirectional filter assembly molded as one-piece.
It is a further object of the present invention to provide a bidirectional filter assembly in which contaminants are flushed from a screening material to allow for self-cleaning of the assembly.